1. Field of the Invention
This invention relates generally to alpha/numeric and graphic displays and, more particularly, to displays in which selected information must be emphasized for the viewer relative to other displayed information.
2. Description of the Related Art
In U.S. patent application Ser. No. 07/432,105 identified above, a technique for processing stored image information to improve the resulting display has been described. The Application addresses the problem of the aliasing of an image. Referring to FIG. 1, a display 101 shows a line 102 with aliasing imposed thereon and the same line 103, processed using anti-aliasing techniques, is shown. Normally, the line 103, on close inspection, is seen to have a smooth profile as shown, but also to have a somewhat fuzzy appearance. The fuzzy appearance is due to the use of gray levels to move the centroid of luminance more precisely up, down, left, or right. The fuzzy appearance is normally not distracting to the viewer and, in all other aspects, the image is judged superior to the aliased image. The fuzziness can be attenuated substantially in direct proportion to the resolution of the display. When the high frequency components are processed without modification, the line 102 has a jagged appearance, each display point (or pixel) exhibiting a binary display characteristic. In addition to the jagged appearance of edges of images, the aliasing phenomenon can result in patterns superimposed on the image. Once again, the frequency response of the display permits the passage of high frequency components of the image in a manner inappropriate to the accurate reproduction of the image.
U.S. patent application No. 07/432,105 provides a solution to the aliasing problem which can be understood with reference to FIG. 2A, FIG. 2B, FIG. 3A, and FIG. 3B. The characteristics of a display pixel are determined on a pixel by pixel procedure based on the optical component characteristics (hereinafter referred to a impulses) of an impulse point stored in the form of electrical signals in image memory. Prior to U.S. Patent Application, when the pixel 25(x,y) was to be activated, the image impulse 20, being associated with pixel 25(x,y), was extracted from the image memory and applied to the circuits controlling the display of pixel 25(x,y) and pixel 25(x,y) was consequently activated to reflect the impulse characteristics. Thus, in FIG. 2B, the pixel 25(x,y) can be represented as having an intensity determined by the intensity of the impulse signal associated with that pixel location. As will be clear to those familiar with display technology, typically three (color) components are associated with each pixel. FIG. 2A and FIG. 2B illustrate only one component for ease of description.
U.S. patent application No. 07/432,105 addresses the aliasing problem by associating with each impulse a distribution which provides that, instead of being localized to one pixel, each impulse contributes to the display of surrounding pixels. Referring to FIG. 3A, a (generally Gaussian) distribution function 35 is shown surrounding the original impulse 20. The illustrated distribution function provides for a contribution not only to the pixel 25(x,y), but also to the neighboring pixels [for example, pixels 25(x-1y), 25(x+1,y), 25(x,y-1), and 25(x,y+1) and sharing a corner with pixel 25(x,y), [i.e., 25(x-1, y-1), 25(x+1,y-1), 25(x-1,y+1), and 25(x+1,y+1)]. Typically the distribution function 35 is 6 to 7 pixels across at the base of the distribution function for a color display. This extent implies coverage of .+-.3 pixels in all directions centering on 25(x,y). Referring to FIG. 3B, the activation of pixel 25(x,y) and the surrounding pixels is illustrated. The neighboring pixels, border sharing pixels in this example, have a display contribution that is less than the contribution to the display of the pixel to which the impulse is assigned, while the pixels sharing corner has an even smaller contribution to the display characteristics in accordance with the distribution function, i.e., in the present example, a Gaussian distribution function.
As will be clear, the extension of the contribution of an impulse to pixels surrounding the pixel to which the impulse has been assigned provides a smoothing of the abrupt transition between the display pixel and an adjoining pixel with no impulse associated therewith. Not only will the abrupt border areas be smoothed, but the high frequency patterns can minimized or eliminated thereby minimizing the aliasing of the image.
Referring to FIG. 4, a block diagram for providing the anti-aliasing of U.S. patent application No. 07/432,105 is shown. The apparatus includes an image memory 41, the image memory 41 having a plurality of memory locations, one location being illustrated by the dotted line region 41A. The memory locations of the image memory store the impulses, in the form of digital data, which ultimately control the display, each image memory location associated with a display pixel or regions of display surface. The contents of image memory locations associated with the display pixel as a result of the distribution function are entered into a two dimensional 3.times.3 shift register where the contents therein access the coefficient memory 42. The coefficient memory stores the weighting coefficients that effect the desired impulse point distribution function. Following the example in FIG. 3A and FIG. 3B, the distribution function is chosen to cause contributions to all impulses in the 3.times.3 window which scans image memory in a manner common to processing of raster scan displays. But that distribution function implies that impulse functions in any cell of the 3.times.3 window centered about the current pixel, the pixel for which the display is being determined, will provide a contribution to the current pixel. Therefore, the coefficient memory 42, in the present example, includes 9 positions, one position for each pixel location from which an associated impulse can provide a contribution to the parameters of the display of the current pixel. For example, in FIG. 4, an impulse 40 is shown, when the current pixel location is 25(x,y), positioned in pixel 25(x-1,y-1). Each location in the pixel memory (of the 9 locations of the present example) has stored therewith coefficients which determine the contribution of an impulse function to the display parameters to be activated for the current pixel. Therefore, each location of the coefficient memory potentially provides a quantity which is contributed to the display of the current pixel: EQU I(i,j)=K(i,j).times.I.sub.p (i,j)ps
where
I.sub.p (i,j) is the intensity of the impulse associated with location (i,j); PA0 K(i,j) is the constant which determines the contribution of I.sub.p (i,j) to the pixel at location (x,y), the impulse being further located within the pixel by an offset (.DELTA.x,.DELTA.y); and PA0 I(i,j) is the contribution of impulse I.sub.p (i,j) to the pixel display at location (x,y). PA0 COM is the algorithm defining how the contributions to the selected pixel are to be combined; PA0 I(x,y) defines the intensity to be applied to pixel(x,y); and PA0 i and j are the indices over which the COM operation is processed, i.e., the selected pixel and the nearest neighboring pixels.
The intensity contributions are then applied to combining unit 43 wherein the contributions to the current pixel display are combined (typically summed): EQU I.sub.I (x,y)=COM[I(i,j)]
where
The quantity I.sub.I (x,y) is then applied to the driver circuits of the current pixel. The driver circuits of the display determine the display, on a pixel by pixel basis, in response to the output signals from the combining unit 43. The timing circuits, not shown, coordinate the application of impulses to the coefficient memory with the driver circuits to ensure the proper display parameters are provided to the current pixel, the current pixel generally being determined by a video raster scan.
U.S. patent application No. 07/432,105 also describes a refinement to the anti-aliasing technique. In this refinement, the graphics generator provides a location of an impulse within a pixel, this position generally referred to as micropositioning the impulse within the pixel. Thus in the image memory 41, each impulse memory location 41A includes a color information in location 41A' and the relative (with respect to the pixel) position of the impulse in location 41A". Referring again to FIG. 4, when an impulse 40 is located at position 40', the contribution to the current pixel 25(x,y) is much less than the when impulse 40 is positioned at location 40'. The use of micropositioning permits the display of the current pixel to take account of that difference. Although the use of micropositioning permits a display more representative of the distribution of impulses, the improved display requires increased complexity of the apparatus. Without micropositioning, the coefficients for each location of the coefficient memory are constant and the contribution to the current pixel is relatively easy to determine, although this implementation is not effective for anti-aliasing applications. With micropositioning, the contribution to the current pixel of an impulse will be a function of the impulse position within the pixel. Therefore, each coefficient memory location must be able to provide the correct functionality for each possible impulse location in the pixel. When a finite number of positions are possible for an impulse within a pixel, a simple memory addressed by the impulse relative location can be used at each coefficient memory location.
The image processing described above, while providing an improved image on the display screen, still must provide a technique for emphasizing certain characters or images that may have importance to a viewer. This emphasis is particularly important in environments such as the cockpit of an aircraft flight deck wherein a bewildering array of data must be provided to the crew of the flight deck, but wherein certain data must be easily identifiable, i.e., data requiring immediate response by the members of the flight deck. In the prior art, display areas have been emphasized by periodic alteration (i.e., flashing) of the intensity of the region of interest. The flashing display can be distracting and a rapid review of this type of display screen can be misinterpreted. Another technique for emphasizing particular information on a display screen is to provide a highlight zone into which the important information is to be displayed. This technique suffers from the concealment of information that would normally be displayed by the screen. This problem is particularly acute in those display applications wherein display screen space is limited, such as in a aircraft cockpit. Similarly, a priority mask, which is created to highlight the portion of the screen display to be accented, will also conceal displayed information which will be particularly significant in situations of limited display screen space. A change in color of the display material can be used to emphasize certain information. However, a difference or change in color is less likely to be detected in many instances than a change in luminance, especially with backgrounds having an arbitrary color. Emphasized information can also be provided with an enhanced luminance. While this technique can provide the requisite enhanced emphasis on the display screen, the lower priority information is displayed with only a fraction of the luminance range and can, therefore, be difficult to interpret.
Referring to FIG. 5, a preferred technique for emphasizing selected display regions is illustrated. The technique, called haloing or providing a halo region, is implemented by surrounding the region to be emphasized with a background border. Specifically in FIG. 5, the characters 458 on display screen 500 are shown without a halo 501 and the characters are shown with a halo 502. As is clear from the FIG. 5, the characters without the haloing 501 can be ambiguous depending on the contrast with background upon which they are superimposed. Regions 505 of different intensity are displayed as display screen background to emphasize the character recognition problem. The characters with the haloing are clearly evident against a variety of backgrounds.
A need has therefore been felt for apparatus and an associated technique which would permit haloing to be incorporated in the anti-aliasing image processing. The inclusion of the haloing processing with the anti-aliasing processing should minimize the irregularities in the border of the halo region and in the interface between the halo region and display region to be emphasized on the display screen.